Adjustable inductance system



g- 1931- I A. GEBHARD 1,817,248

ADJUSTABLE INDUCTANCE SYSTEM Filed July 31. 1929 2 Sheets-Sheet 1 F l4 1:51 E 5/? il x5. 4?

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TORNEY g 4, 1931- i L. A. GEBHARD 1,817,248

ADJUSTABLE INDUCTANCE SYSTEM Filed July 31. 1929 2 Sheets-Sheet 2 1 2 4 24 1] Zn [Hr P] 1: 1- I 24 v INVEN TOR.

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A TTORNEY Patented Aug. 4, 1931 UNITED STATES PATENT OFFICE LOUIS A. GEBHARD, OF \VASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIRED RADIO, INQ, OF NEW YORK, N. Y., A CORPORATION OF DELAWARE ADJUSTABLE INDUCTANGE SYSTEM Application filed July 31, 1929. Serial No. 382,385.

My invention relates broadly to inductance systems generally and more particularly to inductance systems employed in high frequency transmitters.

One of the objects of my invention is to provide an adjustable high frequency inductance system having substantially negligible loss.

Another object of my invention is to provide an inductance system wherein relatively small space is occupied without impairing the efficiency of the inductance system.

Still another object of my invention is to provide a system for introducing cooling fluld in the inductance system of a transmitter in a position of low radio frequency potential for reducing losses inherentin the connecting tubing which supplies and discharges the cooling fluid.

A further object of my invention is to provide a symmetrical arrangement of inductances in a high frequency transmitter having symmetrically distributed capacities and reactances for obtaining balanced operation in combination with an inductance switching system which is fluid cooled.

A still further object of my invention is to provide an ustable inductance system wherein the inter-coupling between the active and non-active inductances is reduced to a substantially minimum value.

A further object of my invention is to provide a frequency changing system for transmitters in which the inductance elements are fluid cooled by a cooling fluid which is introduced at a position adjacent the center of the inductance and distributed to the cooling jackets with a return through a parallel path along the inductance.

Other and further objects of my invent1on are to provide an adjustable inductance system employing certain structural features for increasing the efficiency of inductance systems, a better understanding of which can be had from the specification following and from the accompanying drawings, wherein:

Figure 1 shows a top plan view of the adjustable inductance system of my invention; Fig. 2 is a front view of the arrangement shown in Fig. 1; Fig. 3 shows a side elevation of the inductance system of my invention and Fig. 4 is a schematic circuit diagram showing the electrical connections of the inductance system of my invention in a typical radio transmitter.

In a transmitter which is required to cover a wide range of frequencies, when efficiency is considered, it is necessary to have a number of inductance coils adapted to be successively connected in the circuit at various intervals in the range. The inductance coils should be arranged in such a manner that the coils which are not in use will not interfere with those which are in use at the particular frequency adjustment. The interference which is likely to arise, is due to the coupling of the unused inductance with the inductance used in the circuit at this adjustment. If the unused inductance, together with its distributed capacity, is resonant at the particular frequency on which the transmitter is operating, cei'isiderable loss of efficiency may be expected. Arrangements may be made to have these several inducta-nces disassociated entirely from the circuit when they are not needed for a cer tain frequency adjustment and to have them placed at a considerable distance from the inductance being used. This arrangement necessarily requires considerable available space and does not entirely obviate the (hillculty. In the stated arrangen'icnt, the i".- ductance req ired by the lowest frequency range of the set cannot be used in combination with. the other inductances to provide the particular frequency characteristics of ahigher order, but the required inductance must be supplied by a single coil. The adjustable inductance system of my invention avoids the inefliciency due to coupling loss s between coils, prevents energy loss normally due to increased temperature, and permits the use of the coils for the higher frequency range to be employed in series with other required coils to furnish the necessary inductance in the low r frequency band.

The accompanying drawings illustrate a balanced amplifier output system employing the adjustable inductance s stem of my invention. The top plan View in Fig. 1 shows the liquid cooled tube sockets 1 and 2 in part section. Sockets 1 and 2 are electrically connected to coils 3 and 1, the axes of which are parallel thereto respectively. Coils 3 and v 1 are electrically connected to coils 5 and 6,

respectively. Coils 5 and 6 are placed parallel with respect to each other and at right angles with respect to coils 3 and st. @0115 5 and 6 are electrically connected to coil 7, axis of the latter lying at right angles Lie with respect to the axes of coils 5 and 6 and also at right angles with respect to coils and a. The electrical coupling between C011 7 and the two other coil groups is reduced to a minimum by placing the several coils at a coupling effects. The inductance values of coils 3 and 4 are preferably chosen such that these coils when connected in series will provide the proper inductance for the high frequency range of the circuit. I

In Fig. 3 the condenser 10 which is disposed between the tube sockets 1 and 2 is similar to the arrangement shown and described in my copending application, Serial No. 327,990, filed December 22, 1928. This condenser tunes the circuit comprising the two coils 3 and 1. to the required frequency characteristics. hen the desired frequency characteristics can not be had by the combination of condenser 10 and the coils 3 and st, coils 5 and 6 may be connected in series with the coils 3 and a, respectively. The inducta are values of coils 5 and 6 are chosen such as to provide adjustments for the desired lower frequency band. hen the desired frequency characteristics of the lower order *an not be reached. coil 7 may be connected in the series circuit comprising coils 5 and 6, and 3 and a. The inductance value of coil 7 is preferably chosen such as to give the lowest frequency range desired when connected in circuit with the aforementioned coils.

The control of the connections to the particular coils in the circuit may be accomplished in many different ways. In the ar rangement shown, the control is accomplished through the actuation of handle 11, turning the gear 12, which in turn operates gears 13 and 14 by means of chain Gears 13 and 14c are positioned on shafts 16 and 17, respectively. Switch blades 18 and 19 are carried by shaft 17 and are adapted to engage with cont-acts and 21. Contacts 20 and 21 are mounted atone end of coils 5 and 6, respectively. Switch blades 18 and 19 are electrically connected together through shaft 17. Shafts 16 and 17 are insulated at the ends thereof from the framework of the radio transmitter. Shafts 16 and 17 are set in suitable bearings provided in framework 45. Shaft 16 is arranged with the switch blades 26 and 27 to be associated with contacts 28 and 29 similar to the arrange ment on shaft 17. The switch blades are positioned on the shafts in such a manner that when the handle 11 is revolved, contacts 20 and 21 will close and thus provide the connection required for the highest frequency band of the set. In this connection only coils 3 and 4 are connected in series and comprise the output circuit inductance for thermionic tubes 1 and 2. In effect this position short circuits the coils 5, G and 7. However, since these coils are not in the field of coils 3 and 4; large currents are not built up in them and therefore there is little high frequency loss, If, however, coils 5, 6 or 7 were coupled to coils 3 and 4, in this condition serious losses may be encountered. It may be sufiicient if shields 8 and 9 are not used but these will hel to reduce the coupling where the coils are ciosely grouped. \Vhen coils 5 and 6 are to be inserted in the high frequency circuit, handle 11 is turned to anew position. This is indicated by pointer 24 which is adjacent to a scale on the front panel 25 of the radio transmitter. In this position, the connections between switch blades 18 and 19 and the contacts 20 and 21 are open. The connection between switch blades 26 and 27 and contacts 28 and 29 is closed. This connects coils 5 and (5 in series with coils 3 and 4 respectively for the second frequency band of the set and also short circuits coil 7. The latter causes no serious loss due to the fact that coil 7 is disposed at right angles to and is shielded from the rest of the coils.

The third frequency range of the set is obtained by opening both groups of contacts through operation of handle 11 which connects all coils in series and in the high frequency circuit. Other bands of frequencies may be covered by inserting coils in series similar to the arrangement shown, however it is no longer possible to place the coils at right angles to each other. Ditliculty from coupling in any degree may be further avoided by providing separate metallic compartments for the several coils employed.

The inductance system may be supported in any suitable manner from the framework of the transmitter instead of being mounted as shown in the drawings. The design of the individual coils may be such as to make the turns self supporting. In any event suitable insulation must be provided to prevent voltage breakdown at any point where a diffei ence of potential exists.

Another improvement in the adjustable inductance system of my invention is the method of feeding the liquid cooling supply to the liquid cooled "thermionic tubes clearly shown in Figs. 1 and 3. The liquid is admitted to connector 46 of coil 7 which is at its electrical center. The liquid flow divides and passes equally to both ends of coil 7. From these points it passes through coils and 6 and 3 and 4 into the liquid cooled thermionic tube sockets 1 and 2. After circulating through the sockets 1 and 2, the liquid returns to coils 3 and 4 through a different passage which is immediately adjacent the inlet passage. The flow of the liquid continues through coils 5 and 6 and lastly through coil 7 to its center and discharges at the outlet connector 47. The passages or liquid conductors employed in coils 3, 4, 5, 6 and 7 may be composed of two metallic tubes fastened immediately adjacent each other either side by side or one inside the other so as to provide a single electrical conductor having two liquid paths. This conductor may be of the design shown and described in my copending applications Serial Nos. 327,988, filed December 22, 1928, and

345,740, filed March 9, 1929. Suitable metallic connectors having both the properties of an electrical conductor and a cooling liquid conductor are provided between each of the several coils. The cooling liquid may be admitted to the electrical center of coil 7 and discharged from this point through suitable insulating tubing coils which are not shown in the drawings. Also the anode potential supply for the thermionic tubes may be connected at the high frequency electrical center of coil 7. The insulating coil or coils are connected at this same point and are provided to furnish a path of low resistance for the cooling liquid and a path of relatively high electrical resistance which is in parallel with the anode energy supplied the thermionic tubes.

My arrangement of liquid cooling permits the liquid to be supplied to the inductance system at a point which is at approximately ground potential as far as the high frequency energy is concerned. This necessarily means that the energy loss at this point, due to the connection of the insulating tubes as well as the presence of the liquid itself, is reduced to a negligible value.

A further advantage is that the same liquid is employed for cooling the inductance coils as well as for cooling the anodes of the ther mionic tubes. The electrical features can best be understood by referring to Fig. 4 of the accompanying drawings. This illustrates a schematic circuit diagram of the arrange ment employed.

In addition to the units already described which bear the same reference numbers as employed in the foregoing illustrations, balance condensers and 31 are shown. A choke coil 32 is provided in the anode supply circuit to permit a floating ground at the electrical center 7 a of coil 7. Coupling of the high frequency energy to the output circuit of thermionic tubes 1a and 2m is accomplished by means of condensers 33 and 34. The load circuit consists of transmission line 35 and antenna system 36. Obviously, any type of load circuit may be supplied. If desired inductance coils 3, 4, 5, 6 and 7 may be provided with suitable taps and a switching mechanism whereb the transmission line 35, together with con ensers 33 and 34 in series therewith, may be connected to any of the several coils. This provides a very flexible coupling system by means of which efficient energy transfer at all frequency adjustments is possible. The input circuit of thermionic tubes 1a and 2a consists of condenser 37, inductance 38 and high frequency bypass condenser 39. Coil 38 is coupled with circuit 40 which may be the output circuit of a high frequency oscillator or amplifier. The source of negative biasing potential 41 is provided to obtain the proper operating characteristics of thermionic tubes la. and 2a.

Since the inductance value of coil 3 preferably corresponds to the inductance value of coil 4 it follows that when arm 17 is actuated, thereby connecting contacts 20 and 21, the potential of arm 17 is substantially that of ground potential. Likewise it follows that when arm 16 connects contacts 28 and 29, arm 16 is at substantially ground potential, since coils 5 and 6 are preferably chosen of like inductance values. Arms or control shafts 16and 17 have a very low resistance. By actuating arm 16 and establishing connection between contacts 28 and 29, it follows that potential at the ends of coil 7 is reduced to substantially that of ground potential. that is of course with regard to high fre quency energy. It therefore means that there is substantially no high frequency energy in coil 7 at this adjustment. Since coil 7 is actually positioned at right angles with. respect to coils 3, 4, 5 and 6, substantially no induced currents occur. If the coils were not positioned with their axes at right angles to each other, as shown in Figs. 1, 2, and 3, of the drawings, some induced currents of appreciable value would exist in coil 7. The inductance of coil 7, together with the distributed capacity in the winding, would give the coil certain inherent and resonant frequency characteristics. Should the energy in the output circuit of the thermionic tubes be of the same frequency or a multiple thereof. excessive losses would ensue. This is all avoided in the adjustable inductance system of my invention.

It is not necessary to employ the specific number of inductance coils shown in the drawings. From the foregoing drawings it will be noticed that coils 5 and 6 are not positioned at right angles with respect to each other, and it will be observed that these coils are connected in the same radio frequency circuit at the same time and when one is in use the other is also in use. By reason of the fact that these coils are in the circuit or out of the circuit simultaneously the losses due to unused coils is negligible and reaction between them introduces no difficulty. The gen eral arrangement may consist of either coils 3, 5 and 7 or of coils 4, 6 and 7, in either case each group of coils is positioned at right angles with respect to each other group. When the combined arrangement is employed as shown in the drawings it should be observed that all non-active or unused group of coils are always positioned at right angles with respect to the group of active or used coils thereby avoiding the losses ordinarily incurred.

In order to maintain balanced Operation these coils are placed preferably symmetrically since this gives symmetrical distributed capacities and reactions.

I realize that many modifications are possible without departing from the spirit of my invention. It is to be strictly understood that the embodiments of my invention are not to be restricted by the foregoing specification or by the accompanying drawings, but only by such restrictions as are imposed by the appended claims.

hat I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A high frequency inductance system comprising in combination a plurality of inductance coils the winding of each of said inductance coils consisting of a pair of metallic fluid conducting members, said members interconnected by fluid conducting members and said coils positioned at substantially right angles with respect to each other, whereby cooling fluid may be caused to flow in opposite directions through each of the pair of fluid conducting members constituting a coil, and electrical equilibrium of the system may be maintained.

2. A high frequency inductance system comprising in combination a plurality of helixes positioned substantially at right angles with respect to each other and parallel respectively to the axes of a three dimensional system of rectangular Cartesian coordinates, said helixes consisting of metallic tubing, fluid conducting members interconnecting said helixes, and means for admitting cooling fluid to said heliXes at the electrical center thereof.

3. A high frequency inductance system comprising in combination a plurality of inductance coils the windings of which consist of metallic fluid conducting members, said members interconnected by fluid conducting members, said coils being positioned at substantially 90 with respect to each other and parallel respectively to the axes of a three dimensional system of rectangular Cartesian coordinates, and means for admitting cooling fluid to said coils at the electrical center thereof.

4. A high frequency inductance system comprising in combination a plurality of individual inductance coils electrically connected in series and positioned at substantially right angles with respect to each other and parallel respectively to the axes of a three dimensional system of rectangular Cartesian coordinates, and means for admitting at the electrical center of said coils a cooling fluid through the conductors comprising said inductance coils.

5. A high frequency inductance system comprising in combination a plurality of individual inductance coils electrically interconnected by fluid conducting members and connected in series for the circulation of a cooling fluid through the windings thereof, said inductance coils being positioned at substantially right angles with respect to each other and parallel respectively to the axes of a three dimensional system of rectangular Cartesian coordinates, and means for admitting cooling fluid to said coils at the electrical center thereof.

6. A high frequency inductance system comprising in combination a plurality of inductance coils electrically connected in series, said inductance coils being positioned at sub stantially right angles with respect to each other and means for changing the value of inductance in said inductance system by selectively connecting a low resistance circuit across said coils.

7. A high frequency inductance system comprising in combination a plurality of inductance coils electrically connected in series, said inductance coils being positioned at substantially right angles with respect to each other and means for changing the value of inductance in said inductance system by selec tively connecting a low resistance low inductance shunt across said coils.

8. A high frequency inductance system comprising in combination a plurality of inductance coils electrically connected in series. said inductance coils being positioned at sub stantially right angles with respect to each other and means for changing the value of inductance in said inductance system by selectively connecting a low inductance shunt across said coils.

9. A high frequency inductance system comprising in combination a plurality of inductance coils electrically connected in series, said inductance coils being positioned at sub stantially right angles with respect to each other and means for adjusting the value of inductance in said inductance system by selectively connecting a shunt across one of said coils and across others of said coils in successive order.

10. A high frequency inductance system comprising in combination a plurality of helixes positioned substantially at right angles with respect to each other, said helixes 5 consisting of metallic tubing and fluid conducting members interconnecting said helixes, means for admitting cooling fluid to said helixes at the electrical center thereof, and means for effecting different adjustments of inductance by selectively shunting said helixes in successive order.

11. A high frequency inductance system comprising in combination a plurality of inductance coils the windings of which con- 15 sist of metallic fluid conducting members, said members being interconnected by fluid conducting members, said coils being positioned at substantially 90 with respect to each other, means for admitting cooling fluid as to said coils at the electrical center thereof, and means for effecting different adjustments of inductance by selectively shunting said coils in successive order.

12. A high fredjuency inductance system comprising in com ination a plurality of individual inductance coils electrically connected in series, said inductance coils being tubular and interconnected by fluid conducting members for the circulation of a cooling 30 fluid through the windings thereof, said inductance coils being positioned at substantially right angles with respect to each other, means for admitting cooling fluid to said coils at the electrical center thereof and means for effecting different adjustments of inductance by selectively shunting said coils.

13. In an inductance system, three groups of helical inductance coils, the individual coils of a group being positioned with their 40 axes parallel, said three groups of coils being spacially oriented so that the axes of each of said groups are respectively parallel to a three dimensional system of rectangular Cartesian coordinates, said coils being tubular c5 and interconnected by fluid conducting members for continuously conducting cooling fluid therethrough.

14. In an inductance system, three groups of helical inductance coils, the individual b0 coils of a group being positioned with their axes parallel, said three groups of coils being spacially oriented so that the axes of each of said groups are respectively parallel to a three dimensional system of rectangular iv Cartesian coordinates, said coils being tubular and interconnected by fluid conducting members for continuously conducting cooling fluid therethrough, said coils being electrically connected together, and means for selectively short-circuiting the terminals of each of said coils.

LOUIS A. GEBHARD. 

